Persistence of adaptation following visuomotor training.

Retention tests conducted after sensorimotor adaptation frequently exhibit a rapid return to baseline performance once the altered sensory feedback is removed. This so-called washout of learning stands in contrast with other demonstrations of retention, such as savings on re-learning and anterograde interference effects of initial learning on new learning. In the present study, we tested the hypothesis that washout occurs when there is a detectable discrepancy in retention tests between visual information on the target position and somatosensory information on the position of the limb. Participants were tested following adaptation to gradually rotated visual feedback (15° or 30°). Two different types of targets were used for retention testing, a point target in which a perceptual mismatch is possible, and an arc-target that eliminated the mismatch. It was found that, except when point targets were used, retention test movements were stable throughout aftereffect trials, indicating little loss of information. Substantial washout was only observed in tests with a single point target, following adaptation to a large amplitude 30° rotation. In control studies designed to minimize the use of explicit strategies during learning, we observed similar patterns of decay when participants moved to point targets that suggests that the effects observed here relate primarily to implicit learning. The results suggest that washout in aftereffect trials following visuomotor adaptation is due to a detectable mismatch between vision and somatosensation. When the mismatch is removed experimentally, there is little evidence of loss of information. Aftereffects following sensorimotor adaptation are important because they bear on the understanding of the mechanisms that subserve forgetting. We present evidence that information loss previously reported during retention testing occurs only when there is a detectable discrepancy between vision and somatosensation and, if this mismatch is removed, the persistence of adaptation is observed. This suggests that washout during aftereffect trials is a consequence of the experimental design rather than a property of the memory system itself.